Quickly on this question, it's not the common ancestor we don't know about, it's what came before the common ancestor.
Imagine life begins, and it begins to diversify and speciation occurs (I know I'm asking you to accept this before answering the rest of your questions for the sake of an example). But a large number of those species go extict, and all living organisms are descended from one specific branch of that original family tree. We can't know anything from before that branch of the tree. That's all I mean.
The answer to your first two questions can kind of be handled by the same explanation.
I'm sure you're familiar with genetic testing to determine how closely two humans are related. You can kind of do a similar thing with different species.
First, it's important to understand how DNA works. DNA is essentially a long set of instructions for making different proteins at different times. That's really all it can do.
Proteins are made by taking the information from different segments of DNA. Let's say that a particular DNA segment looks like this "ACTGGGTACG" and it makes "Protein X". It's important to keep in mind that I'm keeping the DNA segment short just for ease of explanation. The way DNA works, sometimes mutations occur. Sometimes these mutations result in the protein being made incorrectly or not at all. That would probably be a fatal defect. Sometimes they are changed in beneficial ways. Most often, they are changed in neutral ways. It's possible for two slightly different segments to make a protein with the same physical structure.
These changes can accumulate because they don't impact the actual usefulness of the protein. If my parents had a mutation that didn't change the protein shape, I will pass it to my children because the protein didn't cause any problems with my health. My kids and their kids will have the same different segment.
This is how the science of evolution can make predictions. In a world where all organisms are related, we should see some structure of relatedness emerge from an analysis for any particular protein.
And it does. For any protein you can pick.
If someone had created all organisms from scratch, what reason would they have to give them slightly different DNA segments for the same proteins that resemble exactly what you'd expect if they had all been related to each other. One answer I can think of is that the creator is a jerk who wants to punish us for using our brain. I don't think that's how most people imagine God.
To summarize, let's imagine 3 the DNA segment for "Protein X" for 3 different organisms. When there's a difference I'll bold it.
1) ACTGGGTACG
2) ACTGGGTACC
3) ACTGGGTAAC
Notice in organism 2, only the last letter is different from organism 1. But in organism 3, the last 2 are different from organism 1, but only 1 is different from organism 2. We can infer that organism 3 is more closely related to organism 2 than organism 1.
This is highly simplified, but you can see how these patterns would emerge from the commonly understood elements of heredity.
Imagine life begins, and it begins to diversify and speciation occurs (I know I'm asking you to accept this before answering the rest of your questions for the sake of an example). But a large number of those species go extict, and all living organisms are descended from one specific branch of that original family tree. We can't know anything from before that branch of the tree. That's all I mean.
The answer to your first two questions can kind of be handled by the same explanation.
I'm sure you're familiar with genetic testing to determine how closely two humans are related. You can kind of do a similar thing with different species.
First, it's important to understand how DNA works. DNA is essentially a long set of instructions for making different proteins at different times. That's really all it can do.
Proteins are made by taking the information from different segments of DNA. Let's say that a particular DNA segment looks like this "ACTGGGTACG" and it makes "Protein X". It's important to keep in mind that I'm keeping the DNA segment short just for ease of explanation. The way DNA works, sometimes mutations occur. Sometimes these mutations result in the protein being made incorrectly or not at all. That would probably be a fatal defect. Sometimes they are changed in beneficial ways. Most often, they are changed in neutral ways. It's possible for two slightly different segments to make a protein with the same physical structure.
These changes can accumulate because they don't impact the actual usefulness of the protein. If my parents had a mutation that didn't change the protein shape, I will pass it to my children because the protein didn't cause any problems with my health. My kids and their kids will have the same different segment.
This is how the science of evolution can make predictions. In a world where all organisms are related, we should see some structure of relatedness emerge from an analysis for any particular protein.
And it does. For any protein you can pick.
If someone had created all organisms from scratch, what reason would they have to give them slightly different DNA segments for the same proteins that resemble exactly what you'd expect if they had all been related to each other. One answer I can think of is that the creator is a jerk who wants to punish us for using our brain. I don't think that's how most people imagine God.
To summarize, let's imagine 3 the DNA segment for "Protein X" for 3 different organisms. When there's a difference I'll bold it.
1) ACTGGGTACG
2) ACTGGGTACC
3) ACTGGGTAAC
Notice in organism 2, only the last letter is different from organism 1. But in organism 3, the last 2 are different from organism 1, but only 1 is different from organism 2. We can infer that organism 3 is more closely related to organism 2 than organism 1.
This is highly simplified, but you can see how these patterns would emerge from the commonly understood elements of heredity.
BS Liberal Arts progress - 105/120
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